Monad -fgl

The Monad class defines the basic operations over a monad, a concept from a branch of mathematics known as category theory. From the perspective of a Haskell programmer, however, it is best to think of a monad as an abstract datatype of actions. Haskell's do expressions provide a convenient syntax for writing monadic expressions.
Minimal complete definition: >>= and return.
Instances of Monad should satisfy the following laws:
> return a >>= k == k a
> m >>= return == m
> m >>= (\x -> k x >>= h) == (m >>= k) >>= h
Instances of both Monad and Functor should additionally satisfy the law:
> fmap f xs == xs >>= return . f
The instances of Monad for lists, Data.Maybe.Maybe and System.IO.IO defined in the Prelude satisfy these laws.

Provides a monad-transformer version of the Control.Exception.catch function. For this, it defines the MonadCatchIO class, a subset of MonadIO. It defines proper instances for most monad transformers in the mtl library.
Version 0.3.0.5

Provides functions to throw and catch exceptions. Unlike the functions from Control.Exception, which work in IO, these work in any stack of monad transformers (from the transformers package) with IO as the base monad. You can extend this functionality to other monads, by creating an instance of the MonadCatchIO class. Warning: this package is deprecated. Use the exceptions package instead, if possible.
Version 0.3.1.0

The strategy of combining computations that can throw exceptions by bypassing bound functions from the point an exception is thrown to the point that it is handled.
Is parameterized over the type of error information and the monad type constructor. It is common to use Either String as the monad type constructor for an error monad in which error descriptions take the form of strings. In that case and many other common cases the resulting monad is already defined as an instance of the MonadError class. You can also define your own error type and/or use a monad type constructor other than Either String or Either IOError. In these cases you will have to explicitly define instances of the Error and/or MonadError classes.

Monads in which IO computations may be embedded. Any monad built by applying a sequence of monad transformers to the IO monad will be an instance of this class.
Instances should satisfy the following laws, which state that liftIO is a transformer of monads:
* . return =
* (m >>= f) = liftIO m >>=
> (liftIO .

Monads in which IO computations may be embedded. Any monad built by applying a sequence of monad transformers to the IO monad will be an instance of this class.
Instances should satisfy the following laws, which state that liftIO is a transformer of monads:
* . return =
* (m >>= f) = liftIO m >>=
> (liftIO .